Method of inducing bone growth using TGF-β

ABSTRACT

A method is provided for generation of bone at a site of an animal where skeletal tissue is deficient comprising administering to the animal, locally at the bone site in the presence of a source of osteogenic cells, an effective amount of a composition comprising TGF-β in a pharmaceutically acceptable carrier, provided that such composition excludes a bone morphogenetic cofactor, the composition being administered in an amount effective to induce bone growth at the bone site. Also provided is a device for implantation into a site of an animal where skeletal tissue is deficient comprising a device treated with an effective amount of a composition comprising TGF-β and a source of osteogenic cells in a pharmaceutically acceptable carrier.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the use of transforming growth factor-beta to induce bone growth in vivo and to devices for implantation into a bony site that are treated with transforming growth factor-beta, as well as to pharmaceutical compositions for this purpose.

2. Description of Related Art

The disorders associated with bone loss present major public health problems for Western societies. Osteoporosis alone may affect 20 million Americans in the early years of the next century. Hence, there is wide interest in identifying factors or potential therapeutic agents that inhibit bone loss and stimulate the formation of healthy new bone.

Bone is an extremely complex, but highly organized, connective tissue that is continuously remodeled during the life of an adult by cellular events that initially break it down (osteoclastic resorption) and then rebuild it (osteoblastic formation). This remodeling process occurs in discrete packets throughout the skeleton, i.e., in both cortical bone and trabecular bone. It has recently been reported that mouse bone marrow cells can be stimulated to generate osteoclasts in the presence of parathyroid hormone-related protein or vitamin D. See Akatsu et al., Endocrinology, 125:20-27 (1989); Takahashi et al., Endocrinology 123:2600-2602 (1988) and Takahashi et al., Endocrinology, 123: 1504-1510 (1988).

The currently available therapeutic agents known to stimulate bone formation are fluoride, estrogen, metabolites, and vitamin D. Fluoride clearly increases trabecular bone mass, but questions remain about the quality of the new bone formed, the side effects observed in some patients, whether there are beneficial effects on vertebral fracture rates, and whether increased fragility of cortical bone with subsequent propensity to hip fracture follows.

Another approach is using agents that promote resorption (parathyroid hormone) and then interrupt resorption (calcitonin). One proposed, but not validated, such sequential therapeutic regimen is coherence therapy, where bone metabolic units are activated by oral phosphate administration and then resorption is inhibited by either diphosphonates or calcitonin.

Within the past few years several factors that stimulate osteoblasts were identified in bone, including TGF-β, fibroblast growth factor, platelet-derived growth factor, insulin-like growth factor I, and β2 macroglobulin. Of these, TGF-β and IGF-I were deemed attractive candidates for factors linking previous bone resorption with subsequent bone formation. Mundy, The Journal of NIH Research, 1:65-68 (1989).

Other proteins stored in the bone matrix may also be important for bone formation. When demineralized bone was injected into the muscle or subcutaneous tissue of rats, a cascade of events, including chondrogenesis, ensued. Urist, Science, 150:893 (1965). This observed activity was due to bone morphogenetic protein (BMP). Since the 1960s several investigators have attempted to identify and characterize this activity. Thus, a protein of 22 Kd, called osteogenin, was identified that possessed the activity. Sampath et al., Proc Natl. Acad. Sci. USA, 84:7109 (1987). Recently, a glycoprotein called osteoinductive factor was purified that exhibited many of the same properties as TGF-β in vitro but which, unlike TGF-β, could induce all of the events involved in the osteoinductive process in vivo. Bentz et al., J. Cell. Biol., 107: 162a (1989). Additionally, three proteins from demineralized ovine bone matrix were identified as having this activity. Wang et al., Proc. Natl. Acad. Sci., 85:9484 (1988) and Wozney et al., Science, 242:1528 (1988). These proteins were named BMP-1, BMP-2A, and BMP-3, the latter two of which belong to the extended TGF-β family by limited sequence homology. These workers modified the assay for bone induction to show cartilage formation but did not show that the proteins ultimately stimulate formation of bone.

The transforming growth factor-beta (TGF-β) group of molecules are each dimers containing two identical polypeptide chains linked by disulfide bonds. The molecular mass of these dimers is about 25 Kd. Biologically active TGF-β has been defined as a molecule capable of inducing anchorage independent growth of target cell lines or rat fibroblasts in in vitro cell culture, when added together with EGF or TGF-α as a co-factor. TGF-β is secreted by virtually all cell types in an inactive form. This latent form can be activated by proteolytic cleavage of mature TGF-β from its precursor (at the Arg-Ala bond in position 278). A non-covalent complex is formed from the association of the mature TGF-β with the precursor remainder or with a protein binding to TGF-β or with alpha₂ -macroglobulin. This complex is disrupted so as to activate the TGF-β either by exposure to transient acidification or by the action of exogenous proteases such as plasmin or plasminogen activator.

There are at least five forms of TGF-β currently identified, TGF-β1, TGF-β2, TGF-β3, TGF-β4, and TGF-β5. Suitable methods are known for purifying this family of TGF-βs from various species such as human, mouse, green monkey, pig, bovine, chick, and frog, and from various body sources such as bone, platelets, or placenta, for producing it in recombinant cell culture, and for determining its activity See, for example, R. Derynck et al., Nature 316:701-705 (1985); European Pat. Pub. Nos. 200,341 published Dec. 10, 1986, 169,016 published Jan. 22, 1986, 268,561 published May 25, 1988, and 267,463 published May 18, 1988; U.S. Pat. No. 4,774,322; Seyedin et al, J. Biol. Chem., 262:1946-1949 (1987); Cheifetz et al, Cell, 48:409-415 (1987); Jakowlew et al., Molecular Endocrin., 2:747-755 (1988); Dijke et al., Proc. Natl. Acad. Sci. (U.S.A.), 85:4715-4719 (1988); Derynck et al., J. Biol. Chem., 261:4377-4379 (1986); Sharples et al., DNA, 6:239-244 (1987); Derynck et al., Nucl. Acids. Res., 15:3188-3189 (1987); Derynck et al., Nucl. Acids. Res., 15:3187 (1987); Derynck et al., EMBO J., 7:3737-3743 (1988)); Seyedin et al., J. Biol. Chem., 261:5693-5695 (1986); Madisen et al., DNA, 7:1-8 (1988); and Hanks et al., Proc. Natl. Acad. Sci. (U.S.A.), 85:79-82 (1988), the entire contents of these publications being expressly incorporated by reference.

TGF-β3, TGF-β4, and TGF-β5, which are the most recently discovered forms of TGF-β, were identified by screening cDNA libraries. None of these three putative proteins has been isolated from natural sources, although Northern blots demonstrate expression of the corresponding mRNAs. TGF-β4 and TGF-β5 were cloned from a chicken chondrocyte cDNA library (Jakowlew et al., Molec. Endocrinol., 2:1186-1195 (1988)) and from a frog oocyte cDNA library, respectively. The frog oocyte cDNA library can be screened using a probe derived from one or more sequences of another type of TGF-β. TGF-β4 mRNA is detectable in chick embryo chondrocytes, but is far less abundant than TGF-β3 mRNA in developing embryos or in chick embryo fibroblasts. TGF-β5 mRNA is expressed in frog embryos beyond the neurula state and in Xenopus tadpole (XTC) cells.

TGF-β has been shown to have numerous regulatory actions on a wide variety of both normal and neoplastic cells. TGF-β is multifunctional, as it can either stimulate or inhibit cell proliferation, differentiation, and other critical processes in cell function (M. Sporn, Science, 233:532 [1986]). For a general review of TGF-β and its actions, see Sporn et al., J. Cell Biol., 105:1039-1045 (1987) and Sporn and Roberts, Nature, 332:217-219 (1988).

The multifunctional activity of TGF-β is modulated by the influence of other growth factors present together with the TGF-β. TGF-β can function as either an inhibitor or an enhancer of anchorage-independent growth, depending on the particular set of growth factors, e.g., EGF or TGF-α, operant in the cell together with TGF-β (Roberts et al., Proc. Natl. Acad. Sci. U.S.A., 82:119 [1985]). TGF-β also can act in concert with EGF to cause proliferation and piling up of normal (but not rheumatoid) synovial cells (Brinkerhoff et al., Arthritis and Rheumatism, 26:1370 [1983]).

Although TGF-β has been purified from several tissues and cell types, as indicated above, it is especially abundant in bones (Hauschka et al., J. Biol. Chem., 261:12665 (1986)) and platelets (Assoian et al., J. Biol. Chem., 258:7155 (1983)). TGF-β is postulated to be one of the local mediators of bone generation and resorption, because of its presence in large amounts in bone and cartilage, because cells with osteoblast and chondrocyte lineage increase replication after exposure to TGF-β, and because TGF-β regulates differentiation of skeletal precursor cells. See Centrella et al., Fed. Proc. J., 2:3066-3073 (1988).

Immunohistochemical studies have shown that TGF-β is involved in the formation of the axial skeleton of the mouse embryo. TGF-β is also present in other embryos in the cytoplasm of osteoblasts in centers of endochondral ossification and in areas of intramembranous ossification of flat bones, such as the calvarium. Heine et al., J. Cell. Biol., 105:2861-2876 (1987). Following in situ hybridization of TGF-β1 probes, localization of TGF-β in both osteoclasts and osteoblasts has been described in development of human long bones and calvarial bones. Sandberg et al., Development, 102:461-470 (1988), Sandberg et al., Devel. Biol., 130:324-334 (1988). TGF-β is found in adult bone matrix (Seyedin et al., Proc. Natl. Acad. Sci. USA. 82:2267-2271 (1985), Seyedin et al., J. Biol. Chem., 261:5693-5695 (1986)) and appears at the time of endochondral ossification in an in vivo model of bone formation (Carrington et al., J. Cell. Biol., 107:1969-1975 (1988)). Cultured fetal bovine bone osteoblasts as well as rat osteosarcoma cells have high mRNA levels for TGF-β and secrete relatively high concentrations of TGF-β (Robey et al., J. Cell. Biol., 105:457-463 (1987)).

In certain in vitro models, TGF-β was found to stimulate the synthesis of collagen, osteopontin, osteonectin, and alkaline phosphatase, and to stimulate replication in osteoblast-like cells. See Centrella et al., J. Biol. Chem., 262:2869-2874 (1987), Noda et al., J. Biol. Chem., 263:13916 (1988), Wrana et al., J. Cell. Biol., 106:915 (1988), Noda et al., J. Cell. Physiol., 133:426 (1987), Pfeilshifter et al., Endocrinology, 121:212 (1987), Centrella et al., Endocrinology, 119:2306 (1986), and Roby et al., J. Cell. Biol., 105:457 (1987). In other in vitro models, TGF-β was found to inhibit proliferation and expression of alkaline phosphatase and osteocalcin. See Centrella et al., supra, Noda and Rodan, Biochem. Biophys. Res. Commun., 140: 56 (1986), and Noda, Endocrinology, 124:612 (1989).

Further, while Centrella et al., supra, showed increased collagen synthesis after treatment of osteoblasts from rat calvaria with TGF-β, Robey et al., supra, could not show increased synthesis of collagen in fetal bovine bone osteoblasts, postulating that the increased collagen production is secondary to the effects of TGF-β on the proliferation of osteoblasts. In organ culture, TGF-β was reported to stimulate bone resorption in neonatal mouse calvarias, but inhibit resorption in the fetal rat long bone system. See Tashjian et al., Proc. Natl. Acad. Sci. USA, 82:4535 (1981) and Pfeilshifter et al., J. Clin. Invest., 82:680 (1988). TGF-β activity was reported to be increased in cultures of fetal rat calvaria and in calvarial cells incubated with stimulators of bone resorption, such as parathyroid hormone, 1,25-dihydroxyvitamin Ds, and IL-1 (Petkovich et al., J. Biol. Chem., 262:13424-13428 (1987), Pfeilschifter and Mundy, Proc. Natl. Acad. Sci. USA, 84: 2024-2028 (1987)). Furthermore, it was reported that TGF-β inhibits the formation of osteoclasts in bone marrow cultures. Chenu et al., Proc. Natl. Acad. Sci. USA, 85:5683-5687 (1988). The showing that TGF-β has effects on both osteoclasts and osteoblasts led Pfeilschifter and Mundy, supra, to propose that it is involved in the strict coupling of the processes of bone resorption and bone formation characteristic of the remodeling process in adult bone. It has also been postulated that the local acidic, proteolytic environment provided by the osteoclasts results in activation of matrix-associated latent TGF-β. Oreffo et al., Calcified Tiss. Internatl., 42: Suppl:A15 (1988).

In view of the conflicting results reported for in vitro activities, it is not clear whether in vitro models can be used to predict the effects of TGF-β on bone formation and resorption in vivo. See Roberts et al., Proc. Natl. Acad. Sci. USA, 82:119 (1985).

Additional references reporting that TGF-β promotes the proliferation of connective and soft tissue for wound healing applications include U.S. Pat. No. 4,810,691 issued Mar. 7, 1989, U.S. Pat. No. 4,774,228 issued Sep. 27, 1988, Ignotz et al., J. Biol. Chem., 261:4337 [1986]; J. Varga et al., B.B.Res.Comm., 138:974 [1986]; A. Roberts et al., Proc. Natl. Acad. Sci. U.S.A., 78:5339 [1981]; A. Roberts et al., Fed. Proc., 42:2621 [1983]; and U.S. Pat. No. 4,774,228 to Seyedin et al. TGF-β stimulates the proliferation of epithelia (T. Matsui et al., Proc. Natl. Acad. Sci. U.S.A., 83:2438 [1986]; G. Shipley et al. Cancer Res., 46:2068 [1986]); induces collagen secretion in human fibroblast cultures (Chua et al., J. Biol. Chem., 260:5213-5216 [1983]); stimulates the release of prostaglandins and mobilization of calcium (A. Tashjian et al., Proc. Natl. Acad. Sci. U.S.A., 82:4535 [1985]); and inhibits endothelial regeneration (R. Heimark et al., Science, 233:1078 [1986]).

In wound chambers implanted subcutaneously, TGF-β increased DNA and collagen production. Sporn et al., Science, 219:1329 (1983) and Sprugel et al., Am. J. Pathol., 129:601 (1987). Moreover, TGF-β produced collagen fibrosis when injected subcutaneously (Roberts et al., Proc. Natl Acad. Sci. USA, 83:4167-4171 (1986)) and promoted healing of skin incisions in rats (Mutoe et al., Science, 237:1333 (1987)). Nevertheless, although TGF-β induced chondrogenesis in muscle-derived cells in vitro (Seyedin et al., Proc. Natl. Acad. Sci. USA, 82:2267 (1985) and Seyedin et al., J. Biol. Chem., 261:5693 (1986)), it did not produce cartilage in vivo even when implanted with collagenous substrates, a system used for a long time as a bone induction model in animals (Sampath et al., Proc. Natl. Acad. Sci. USA, 84:7109 (1987) and Howes et al., Calcif. Tissue Int., 42:34 (1988)).

New studies have shown a time-dependent appearance of mRNA for TGF-β1 at a fracture site in a rat and have localized the peptide immunohistochemically in the periosteum of the healing fracture; the same researchers reported that injections of TGF-β1 into the periosteal area of the femur of young rats have caused significant formation of new cartilage. Bolander et al., New York Academy of Sciences, "Transforming Growth Factor-βs: Chemistry, Biology and Therapeutics, May 18-20, 1989. It has been found that injections of TGF-β1 into the parietal bone of young rats stimulated periosteal bone formation, resulting in a thickening of the calvarium. Noda et al., J. Cell. Biol., 107:48 (1988). TGF-β was reported to stimulate local periosteal woven bone formation when injected daily onto the periostea of parietal bones of neonatal rats. Noda and Camilliere, Endocrinology, 124:2991-2994 (1989).

Certain researchers have found that TGF-β does not induce bone formation unless it is administered concurrently with a cofactor, e.g., an osteoinductive factor purified from bovine demineralized bone. Bentz et al., supra, U.S. Pat. No. 4,843,063 issued Jun. 27, 1989 to Seyedin et al., and U.S. Pat. No. 4,774,322 issued Sep. 27, 1988.

The above studies are inconclusive and inconsistent regarding the formation of mature, histologically normal bone with TGF-β alone. For example, the bones being generated by Noda et al., 1989, supra, were neonatal, i.e., not fully formed with large spaces and increased cartilage formation. In addition, woven bone is resorbed before mature bone is laid down. Thus there is still a demonstrated need for a bone induction agent that will induce bone only where it is needed, does not have side effects in some patients as does fluoride treatment, and does not require addition of a cofactor or another peptide growth factor for acceleration of repair of damaged bone in vivo.

Accordingly, it is an object of the present invention to provide exogenous TGF-β to a local site on an animal where skeletal (bony) tissue is deficient without administering a bone-inducing cofactor so as to produce in every case mature, morphologically normal bone at the site of administration where it is needed.

It is another object to provide a device for implantation into an animal for generation of bone that is treated with TGF-β in such a way as to induce bone at the implantation site.

These and other objects will become apparent to those skilled in the art.

SUMMARY OF THE INVENTION

The above objects are achieved by providing a method for generation of bone at a site of an animal where skeletal tissue is deficient comprising administering to the animal, locally at the site in the presence of an osteogenic cell source, an effective amount of a composition comprising TGF-β in a pharmaceutically acceptable carrier, provided that such composition excludes a bone morphogenetic cofactor, the composition being administered in an amount effective to induce bone growth at the site.

In another aspect, the invention provides a device for implantation into a site of an animal where skeletal tissue is deficient comprising a device treated with an effective amount of a composition comprising TGF-β and an osteogenic cell source in a pharmaceutically acceptable carrier.

In a still further aspect, the invention provides a pharmaceutical composition for treatment of a site of an animal where skeletal tissue is deficient comprising an effective amount of TGF-β and an osteogenic cell source in a pharmaceutically acceptable carrier.

These aspects of the invention enable the generation of normal mature bone every time only where it is required at a particular site, without having to add a specific bone-inducing cofactor to ensure bone formation. Preclinical results with TGF-β applied topically as described below show new bone formation in the presence of perichondrium in a rabbit, new bone formation surrounding ceramic implants in bone defects in a rat, and bone formation in a primate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B together illustrate the sequences of human TGF-β1, human TGF-β2, human TGF-β3, chick TGF-β4, and frog TGF-β5.

FIG. 2 illustrates the percentage of wounds with bone formation when placebo (left-most bar), recombinant human TGF-1 (rhTGF-β1) at 25 ng/wound (middle bar), or rhTGF-β1 at 100 ng/wound (right-most bar) is applied in the rabbit ear ulcer model at 42 and 70 days after wounding Maximum bone formation was observed at day 42.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A. Definitions

By "inducing bone growth" is meant promoting the formation of morphologically normal, mature bone only at a site where there is a bone deficiency that needs to be replaced. Mature bone is bone of any type, whether cortical or trabecular, that is mineralized as opposed to immature or cartilaginous bone as would be formed in a neonatal model. Morphologically normal bone is bone that is detected histologically as normal (i.e., consisting of endochondral or membranous type lamellar bone and including marrow spaces with osteoblasts and osteoclasts). This is in contrast, for example, to callous formation with a fibrotic matrix as seen in the first stage of fracture healing. Thus, the bone induction herein is contemplated not only as acceleration of bone regeneration, as in a fracture, but also as stimulation of the formation of bone that is returned to its normal morphological state.

By "skeletal tissue deficiency" is meant a deficiency in bone at any site where it is desired to restore the bone, no matter how bone deficiency originated, e.g., whether as a result of surgical intervention, removal of tumor, ulceration, implant, or fracture.

By "bone morphogenetic cofactor" is meant a protein originally found in the bone matrix that induces all of the cascade events involved in the osteoinductive process in vivo, including chondrogenesis, vascular invasion, formation of a marrow cavity, and eventually formation of a bone ossicle. Such factors include the bone morphogenetic proteins as found in demineralized bone (Urist, Science, 150:893 (1965)), osteogenin, a 22 Kd protein with this activity (Sampath et al., Proc. Natl. Acad. Sci. USA, 84:7109 (1987)), a glycoprotein called osteoinductive factor (U.S. Pat. No. 4,843,063, supra), and BMP-1, BMP-2A, and BMP-3 from demineralized ovine bone matrix (Wang et al, Proc. Natl. Acad. Sci. USA, 85: 9484 (1988) and Wozney et al., Science, 242:1528 (1988)), the disclosures of all of which references are incorporated herein by reference.

The osteoinductive cofactor described in the U.S. patent is isolated from bone, preferably a bovine metatarsal bone, wherein the demineralized bone is prepared, noncollagenous proteins are extracted from the bone, the extract is subjected to gel filtration, the fraction constituting a low molecular weight (10,000-40,000 daltons) possessing the greatest chondrogenic activity is subjected to ion-exchange chromatography, the first fraction CM-1 is subjected to RP-HPLC, and two peaks of predominantly 28 Kd and 36 Kd chondrogenic/osteogenic cofactor protein are purified to give single bands on SDS-PAGE. These cofactors and the others mentioned above are included in the term "bone morphogenetic cofactor."

By "osteogenic cell source" is meant a source of viable cells that are capable of forming bone, as well as viable cells that are precursors to cells capable of forming bone. Suitable such sources include dispersed whole bone marrow cells (obtained by, e.g., aspiration or mechanical agitation), perichondrium, periosteum, or a suitable cell line. For example, the cells may be taken from a site of the animal to be treated adjacent to the deficiency (e.g., periosteum stripped from an adjacent site to the defect such as a fracture site or a surgical excision site) or from a biopsy site of the animal (e.g., one that has been previously accessed, e.g., the hip).

By "animal" is meant any animal having a vertebrate structure, preferably a mammal, and most preferably a human.

By "TGF-β" is meant the family of molecules described hereinabove that have either the full-length, native amino acid sequence of any of the TGF-βs from any species, including the latent forms and associated or unassociated complex of precursor and mature TGF-β ("latent TGF-β"). Reference to such TGF-β herein will be understood to be a reference to any one of the currently identified forms, including TGF-β1, TGF-β2, TGF-β3, TGF-β4, and TGF-β5 and latent versions thereof, as well as to TGF-β species identified in the future, including polypeptides derived from the sequence of any known TGF-β and being at least 75% homologous with the sequence. Members of the TGF-β family are defined as those which have nine cysteine residues in the mature portion of the molecule, share at least 65% homology with other known TGF-β sequences in the mature region, and compete for the same receptor. In addition, they all appear to be encoded as a larger precursor that shares a region of high homology near the N-terminus and shows conservation of three cysteine residues in the portion of the precursor that will later be removed by processing. Moreover, the TGF-βs appear to have a four or five amino acid processing site.

B. Modes for Carrying Out the Invention

The invention is carried out in one aspect by mixing the TGF-β with a suitable pharmaceutical carrier, and without the bone morphogenetic cofactor, and administering the resulting composition locally to a site on an animal where it is desired to induce formation of normal, adult bone and where a source of osteogenic cells and their precursor cells are present at the site. If the site does not naturally have a source of osteogenic cells present, the pharmaceutical composition also contains an osteogenic cell source as defined above, in an amount sufficient to induce bone growth.

Examples of indications where promotion of bone repair at a skeletal site is important include periodontal disease where root socket healing is impaired (tooth socket sites), non-union fractures, including primary treatment of high risk fractures and adjunctive treatment with bone grafting or bone substitutes for established non-union fractures, large bony defects caused by trauma or surgery [e.g., partial mandibular resection for cancer, large cranial defects, spinal (vertebral) fusions, correction of severe scoliosis by surgical alignment held in place with a Harrington bar (to shorten the six months normally required for a body cast), and spinal fractures with open reduction (to decrease significantly the period of immobilization)], and rapid stabilization and enhanced fixation of artificial prostheses and spacer bars, oral joints, and bone replacements.

Examples of the latter include plastic and reconstructive surgery, fixation of permanent dentures into mandible, enhanced fixation of accepted joint prosthesis, e.g., hips, knees, and shoulders (leading to the acceptance of prostheses that until now have been unacceptable due to rapid loosening and instability such as elbows), and limb salvage procedures, usually associated with malignancy (the bone shaft may be removed but the articular surfaces are left in place and connected by a space bar; rapid and enhanced fixation is required for success). If the site constitutes a periodontal site, i.e., one that involves the teeth, gums, and dental sockets, the TGF-β is administered in conjunction with an exogenously added source of osteogenic cells.

In one preferred embodiment, the TGF-β is administered by treating a device with the TGF-β composition and implanting the device into the animal at the site of the deficiency, the composition also containing the osteogenic cell source when the site is deficient in such cells. The device may consist of any device suitable for implantation, including a molded implant, plug, prosthetic device, capsule, titanium alloy, sponge, or ceramic block. Examples of suitable delivery vehicles useful as devices are those disclosed by Nade et al., Clin. Orthop. Rel. Res., 181: 255-263 (1982); Uchida et al., J. Biomed. Mat. Res., 21:1-10 (1987); Friedenstein et al., Exp. Hematol., 10:217-227 (1982); Deporter et al., Calcif. Tissue Int., 42:321-325 (1988); McDavid et al., J. Dent. Res., 58:478-483 (1979); Ohgushi et al., J. Orthopaedic Res., 7:568-578 (1989), Aprahamian et al., J. Biomed. Mat. Res., 21:965-977 (1986); Emmanual et al., Stain. Tech., 62: 401-409 (1987), the disclosure of all of which references is incorporated herein by reference.

For bone defects involving gaps, such as a dry socket or non. union fracture, a plug may be used to fill the gap. The plug may be composed of, for example, hydroxyapatite or collagen on which TGF-β is adsorbed. For larger bone defects resulting from, e.g., trauma or skeletal reconstruction around an ulcer or hip prosthesis, the device is preferably a made-to-fit ceramic block. More preferably, the ceramic block comprises 0-100% hydroxyapatite and the remaining 100-0% tricalcium phosphate, by weight, most preferably 60% hydroxyapatite and 40% tricalcium phosphate.

In a specific embodiment for a jaw implant, a calcium carbonate moldable material or Interpore™ molding device is molded to fit the jaw using a 3.dimensional x-ray of the jaw before surgery, and the molded material is impregnated with TGF-β. Then, dispensed bone marrow from another site of the animal (e.g., from the hip) is infiltrated into the mold, and the mold is placed into the jaw for final implantation.

Preferably, the device is treated with the TGF-β composition (which includes both a solution and a gel formulation) for a sufficient period of time to allow adsorption, and to allow drying in the case of the gel. The concentration of TGF-β in the solution or gel and the time of exposure depend on a number of factors, including the volume of the defect, the potency of the TGF-β polypeptide, and the nature of the site to which it is applied, and will be adjusted accordingly. As the size of the defect increases, or when the site is other than a bone site, the concentration of TGF-β and the time of presoaking should be increased. The treatment is for preferably at least about 0.5 hour, depending on the factors mentioned above (more preferably at least about 1 hour. and most preferably 1-2 hours), before implantation. Also depending on the above considerations, the concentration of TGF-β in the TGF-β composition is preferably at least about 1 ng/ml (more preferably at least about 1-10 up to 100 ng/ml). The treatment may consist of any mode by which the composition is applied to the device to deliver effectively the TGF-β and the osteogenic cell source. Such treatment includes, for example, adsorption, covalent crosslinking, or impregnation, depending in part on the nature of the indication.

The TGF-β compositions to be used in the therapy will be dosed in a fashion consistent with good medical practice taking into account the nature of the skeletal tissue deficiency to be treated, the species of the host, the medical condition of the individual patient, the presence of any other cotreatment drug in the composition, the site of delivery of the agent, the method of administration, the scheduling of administration, and other factors known to practitioners. Because of differences in host response, significant site-to-site and patient-to-patient variability exists. For purposes herein, the "therapeutically effective amount" of TGF-β is an amount that is effective to induce bone growth, as defined above, at the site of skeletal tissue deficiency.

As a general proposition, the TGF-β is formulated and delivered to the target site at a dosage capable of establishing at the site a TGF-β level greater than about 0.1 ng/cc. Typically, the TGF-β concentrations range from about 0.1 ng/cc to 5 mg/cc, preferably from about 1 to 2000 ng/cc. These intra-tissue concentrations are maintained preferably by topical application and/or sustained release.

As noted above, these suggested amounts of TGF-β are subject to a great deal of therapeutic discretion. The key factor in selecting an appropriate dose and scheduling is the result obtained. Clinical parameters to determine an endpoint include increase in bone formation and mass and in radiographically detectable bone height. Such measurements are well known to those clinicians and pharmacologists skilled in the art.

The TGF-β composition is administered by any suitable means locally to the site, including topical and continuous release formulation. The active TGF-β ingredient is generally combined at ambient temperature at the appropriate pH, and at the desired degree of purity, with a physiologically acceptable carrier, i.e., a carrier that is non-toxic to the patient at the dosages and concentrations employed. The carrier may take a wide variety of forms depending on the form of preparation desired for administration.

To be effective, the TGF-β is converted by the body to its activated form, i.e., the mature form is cleaved from its precursor using a suitable enzyme and the resultant complex is treated with acid or other appropriate agent, to activate the TGF-β. Nevertheless, TGF-β is suitably administered in an inactive or delayed release form such as a complex of mature TGF-β with proTGF-β not containing mature TGF-β (i.e., the remaining precursor of TGF-β), with a TGF-β binding protein, or with alpha-macrzoglobulin. The latent form is then converted to the active form either by naturally occurring mechanisms in the local environment or by formulation with TGF-β activating agents described above. See, e.g., Gentry et al., Mol. Cell. Biol., 8:4162-4168 (1988); Miyazono et al., J. Biol. Chem., 263:6407-6415 (1988); Wakefield et al., J. Biol. Chem., 263:7646-7654 (1988); Keski-Oja et al., J. Cell Biochem. Suppl., 11A:60 (1987); Kryceve-Martinerie et al., Int. J. Cancer, 35:553-558 (1985); Lawrence et al., Biochem. Biophys. Res. Commun., 133:1026-1034 (1985); Lawrence et al., J. Cell Physiol., 121:184-188 (1984). Thus, the pH of the TGF-β composition may suitably reflect the conditions necessary for activation.

For the preparation of a liquid composition suitable for impregnation of a device, the carrier is suitably a buffer, a low molecular weight (less than about 10 residues) polypeptide, a protein, an amino acid, a carbohydrate including glucose or dextran, a chelating agent such as EDTA, a cellulose, or other excipient. In addition, the TGF-β composition is preferably sterile. Sterility is readily accomplished by sterile filtration through (0.2 micron) membranes. TGF-β ordinarily will be stored as an aqueous solution, as it is highly stable to thermal and oxidative denaturation, although lyophilized formulations for reconstitution are acceptable.

Generally, where the bone disorder permits, one should formulate and dose the TGF-β for site-specific delivery, where the TGF-β is formulated into a sterile sustained-release composition suitable for local application to the desired site.

For local application of the TFG-β composition, for example, in case of a bone defect that is a crack, e.g., a union fracture, the carrier may be any vehicle effective for this purpose. For obtaining a gel formulation, the liquid composition is typically mixed with an effective amount of a water-soluble polysaccharide, polyethylene glycol, or synthetic polymer such as polyvinylpyrrolidone to form a gel of the proper viscosity to be applied topically. The polysaccharide is generally present in a gel formulation in the range of 1.90% by weight of the gel, more preferably 1 20%. Examples of other suitable polysaccharides for this purpose, and a determination of the solubility of the polysaccharides, are found in EP 267,015, published May 11, 1988, the disclosure of which is incorporated herein by reference.

The polysaccharide that may be used includes, for example, cellulose derivatives such as etherified cellulose derivatives, including alkyl celluloses, hydroxyalkyl celluloses, and alkylhydroxyalkyl celluloses, for example, methylcellulose, hydroxyethyl cellulose, carboxymethyl cellulose, hydroxypropyl methylcellulose, and hydroxypropyl cellulose; starch and fractionated starch; agar; alginic acid and alginates; gum arabic; pullullan; agarose; carrageenan; dextrans; dextrins; fructans; inulin; mannans; xylans; arabinans; chitosans; glycogens; glucans; and synthetic biopolymers; as well as gums such as xanthan gum; guar gum; locust bean gum; gum arabic; tragacanth gum; and karaya gum; and derivatives and mixtures thereof. The preferred gelling agent herein is one that is inert to biological systems, nontoxic, simple to prepare, and not too runny or viscous, and will not destabilize the TGF-β held within it.

Preferably the polysaccharide is an etherified cellulose derivative, more preferably one that is well defined, purified, and listed in USP, e.g., methylcellulose and the hydroxyalkyl cellulose derivatives, such as hydroxypropyl cellulose, hydroxyethyl cellulose, and hydroxypropyl methylcellulose. Most preferred herein is methylcellulose.

The polyethylene glycol useful for gelling is typically a mixture of low and high molecular weight polyethylene glycols to obtain the proper viscosity. For example, a mixture of a polyethylene glycol of molecular weight 400-600 with one of molecular weight 1500 would be effective for this purpose when mixed in the proper ratio to obtain a paste.

The term "water soluble" as applied to the polysaccharides and polyethylene glycols is meant to include colloidal solutions and dispersions. In general, the solubility of the cellulose derivatives is determined by the degree of substitution of ether groups, and the stabilizing derivatives useful herein should have a sufficient quantity of such ether groups per anhydroglucose unit in the cellulose chain to render the derivatives water soluble. A degree of ether substitution of at least 0.35 ether groups per anhydroglucose unit is generally sufficient. Additionally, the cellulose derivatives may be in the form of alkali metal salts, for example, the Li, Na, K, or Cs salts.

In a preferred embodiment, the gel contains about 2-5% by weight methylcellulose and the TGF-β is present in an amount of about 10-1000 μg per ml of gel. More preferably, the gel consists of about 3% methylcellulose by weight, lactic acid to pH 5.0, and 20-200 μg per ml of TGF-β. This corresponds to a dose of 1.10 μg of TGF-β per 50 μl of gel.

For the preparation of a sustained-release formulation, the TGF-β is suitably incorporated into a biodegradable matrix or microcapsular particle. A suitable material for this purpose is a polylactide, although other polymers of poly (α-hydroxycarboxylic acids), such as poly-D-(-)-3-hydroxybutyric acid (EP 133,988A), can be used. Additional biodegradable polymers include poly(lactones), poly(acetals), poly(orthoesters) or poly(orthocarbonates). The TGF-β is also suitably mixed with a biodegradable protein carrier such as collagen, atelocollagen, or gelatin to form a carrier matrix having sustained-release properties; the resultant mixture is then dried, and the dried material is formed into an appropriate shape, as described in U.S. Pat. No. 4,774,091.

The initial consideration here must be that the carrier itself, or its degradation products, are non-toxic in the target bone site and will not further aggravate the condition. This can be determined by routine screening in animal models of the target bone disorder or, if such models are unavailable, in normal animals. For examples of sustained-release compositions, see U.S. Pat. No. 3,773,919, EP 58,481A, U.S. Pat. No. 3,887,699, EP 158,277A, Canadian Patent No. 1176565, U. Sidman et al., Biopolymers 22:547 (1983), and R. Langer et al., Chem. Tech., 12:98 (1982).

Controlled delivery of TGF-β to a site also is suitably accomplished using permeable hollow cellulose acetate fibers with the TGF-β and placed in the site and removed 24 hours later or left for longer periods of time (U.S. Pat. No. 4,175,326). Also, acrylic resin strips or cast films can be impregnated with TGF-β and applied to the affected site. In addition, narrow dialysis tubing can be filled with a TGF-β solution and placed so as to deliver TGF-β to the appropriate site.

The composition herein also may suitably contain other peptide growth factors such as IGF-I, TGF-α, human growth hormone, epidermal growth factor, and PDGF, provided that such factors do not include the bone morphogenetic factors defined above. Such growth factors are suitably present in an amount that is effective for the purpose intended, i.e., to promote formation of bone.

The invention will be more fully understood by reference to the following examples. They should not, however, be construed as limiting the scope of the invention. All literature citations are incorporated by reference.

EXAMPLE 1

The TGF-β1 used herein was the recombinant expression product of transfected human 293 cells as described by EP 200,341, supra, and by Derynck et al., Nature, 316:701-705 (1985). The individual samples of recombinant human TGF-β1 (rhTGF-β1) were sterilely prepared in methylcellulose containing 20 mM sodium acetate buffer at pH 5.0 and applied as a single topical dose. Selected concentrations of rhTGF-β1 were mixed with methylcellulose gel so that the final concentration of methylcellulose was 3%. The vehicle was formulated in a similar manner without rhTGF-β1 as a control. The material was stored at 5° C. until use.

The rat incisional model utilized young adult Simonsen Albino rats (300-350 g). Full thickness skin incisions were made by cutting through the subdermal panniculus carnosus musculature following Betadine and 70% alcohol scrubbing to sterilize the wound. Two pairs of symmetrical transverse incisions (approximately 2.5 cm) were placed in each animal. A single dose of rhTGF-β1 in methylcellulose was placed into each stainless steel sutured wound by inserting a 25-gauge needle along the edge of the wound and below the sutures. The volume of rhTGF-β1 in 3% methylcellulose placed into each wound was 0.05 ml. Each rat had two incisions into which rhTGF-β1 in 3% methylcellulose was applied. One incision received either vehicle alone (3% methylcellulose) or no treatment at all. Concentrations of rhTGF-β1 were 500, 1000, 2000, or 4000 ng/ml. Dose response curves were developed using dose ranges of 5 to 10,000 ng/wound. Animals were euthanized on day 5, 7, 10, 14, 21, and 28. The entire dorsal skin was excised after the sutures were removed. Two 8-mm wide strips of skin were collected from each incision and fixed in 10% neutral buffered formalin for seven days.

New Zealand white male rabbits (2.5-2.8 kg) were purchased from Elkhorn rabbitry. Anesthesia was induced by an intramuscular injection of ketamine hydrochloride/xylazine hydrochloride mixture. After removal of hair from the ears, the area of the wound was sterilely prepared using Betadine with an alcohol rinse. A circular 6-mm punch biopsy instrument was used to produce wounds to the depth of the ear cartilage. The underlying perichondrium was removed with a periosteal elevator and fine scissors. Wounds were treated with 0.025 ml of 3% methylcellulose or 5, 15, 25, 100, 500, or 1000 ng of rhTGF-β1 in 3% methylcellulose (control). Opsiter™ surgical dressing was placed over each wound. An Elizabethian collar was placed around the neck of the rabbits to prevent mechanical disruption of the wounds by the rabbit.

Studies were also designed to examine short-term and long-term effects of topical rhTGF-β1. Wounds were harvested on days 3, 5, 7, 14, 21, 28, 42, 56, and 70. Wounds were photographed, cut into hemisections, and fixed in 10% neutral buffered formalin for histology and morphometric analysis. Morphometric analysis included measurements of total healing wound area, closing wound area, upper wound gap, lower wound gap, area of collagen, area of granulation tissue, epithelial cell layer length, and bone formation. These measurements were made on the Bioquant System IV analyzer.

The rabbit ear ulcers were examined for delayed effects of rhTGF-β1 on days 21, 28, 42, 56, and 70 following a single application of 25 or 100 ng/wound on the day of wounding. Bone formation was observed along the wound edges and immediately adjacent to the cartilage. The bone was normal in morphological appearance, consisting of endochondral or membranous type bone and ossification with marrow spaces. Osteoblasts and osteoclasts were present. The percentage of wounds with bone increased to a maximum of 74% of the treated wounds at day 42 (100 ng/wound) and decreased to 69% by day 70. See FIG. 2. Bone formation was observed in less than 12% of placebo-treated wounds.

No bone formation was observed in the rat incision model, indicating that bone formation is induced only at a site that has a source of precursor (osteogenic) cells, in this case in the rabbit ear model where the wound was adjacent to perichondrium.

EXAMPLE 2

A rat femur gap model was employed wherein a polyethylene plate 2 mm thick, 8-10 mm long, and 4-5 mm wide was pinned to one face of a rat femur with stainless steel pins. From the center of the femur a 5-8 mm long piece of bone was removed. The plate serves to keep the gap in bone separated. This model is intended to mimic a nonunion fracture in a human.

Set into the gap in the femur is a porous cylindrical 200-400 micron ceramic implant of 60% by weight hydroxyapatite and 40% by weight tricalcium phosphate (Zimmer Inc.), which is either (1) implant alone, (2) implant presoaked for 1 hour in a solution of 50 ng/ml TGF-β1 prepared as described in Example 1 and formulated in Delbecco's medium without serum, (3) implant plus dispersed whole bone marrow cells obtained from syngeneic rat, and (4) implant plus dispersed whole bone marrow cells pretreated with 50 ng/ml of the TGF-β1 in Delbecco's medium described above. A total of 15 rats were used for each of these four groups. One month after implant, the rats were sacrificed and analyzed for histological changes.

Preliminary results indicate that no bone replacement was observed in the control without cells or TGF-β nor with TGF-β without cells; TGF-β with cells was found to accelerate the rate of bone growth over cells alone. The bone formed with TGF-β was found in the interstices of the pores in the ceramic and bridged the gap. The bone formed with the TGF-β was found to be histologically normal.

EXAMPLE 3

A case study was performed using baboons to investigate the effect of TGF-β on bone wound healing. The baboon was selected because of the close analogy of its bone kinetics to those of man. A methylcellulose gel of TGF-β1 was delivered via an analytical bone implant, and after 22 days the implant was removed from the baboon. Tissue obtained from TGF-β implant sites was analyzed using quantitative histomorphometry to determine the mean effect of TGF-β on bone wound healing. Detailed non-quantitative histopathologic evaluation was also performed.

More specifically, four male baboons were implanted with four titanium analytical bone implants (cages) each, two per tibia in areas of close structural geometry. Holes were drilled in the tibia to allow implantation. After implantation, the baboons were allowed to heal for 41 days. On the 41st day, all the implant sites were surgically exposed, tissue was removed, and the test materials were implanted into the implant cores. Each animal received a normal (no treatment) control, a control with only methylcellulose vehicle, and a low (1 μg rhTGF-β in methylcellulose) or high (10 μg rhTGF-β in methylcellulose) dosage of active TGF-β. Specifically, these formulations each consisted of 1 g of 3.0% methylcellulose by weight, lactic acid QS to pH 5.0, and 0, 20, or 200 μg/ml of rhTGF-β1 prepared as described in Example 1. The formulations were poured into size 5 gelatin capsules (Elanco), which were then placed in the core of the titanium implant and used to deliver 50 μl of each formulation, with slow dissolution of the capsule. All implant sites within an animal were randomly assigned to one of the four treatments.

Following 22 days of healing, tissue in all implants was retrieved. The tissue samples were placed in 10% formalin solution, buffered to a pH of 7.0, containing formaldehyde at 3.7% for fixation. Samples were submitted for histopathologic analysis.

The following descriptive and quantitative observations were made:

1. Bone volume in TGF-β sites was lower than control and placebo sites, although not statistically significant.

2. Osteoblast numbers, volume, and activity were significantly greater in the TGF-β sites when compared to either the control or placebo.

3. Osteoclast numbers and activity appeared higher in all four treatment sites when subjectively compared to control data obtained in previous studies.

4. Residual methylcellulose was noted and appeared to require phagocytosis before new trabecular bone could form.

5. TGF-β in the presence of methylcellulose matrix was associated with increased numbers of fibroblast, osteoprogenitor cells, and osteoblasts.

6. No foreign body response or other adverse pathologic reaction to either matrix alone or matrix and TGF-β was observed.

7. Significant periosteal new bone formation was noted over the implants in five TGF-β sites in three animals. Bone formation over the implant to this degree had never been observed in over 450 titanium implant procedures carried out over the past few years.

8. TFG-β sites were identified during blinded histologic review in seven out of a total of eight sites.

9. Methylcellulose sites were identified during blinded histologic review 100% of the time.

Control samples analyzed in this study demonstrated that cancellous tissue formed in the titanium implant is stratified from inferior to superior aspects of the implant core. The superior portion of the tissue (closest to the cap of the titanium implant) is less mature and shows greater osteoblastic activity, while tissue near the inferior aspects of the implant and deep within the medullary compartment is more mature in morphology and shows a reduced osteoblastic population and activity. In contrast to historical and control samples, the TGF-β tissue samples were homogeneous in their high osteoblastic activity throughout the specimen.

Clinical observations of the tissue above and around the supraperiosteal portion of the titanium implant revealed pronounced periosteal bone formation. This periosteal bone formed large masses over two sites in each of two animals. The masses in these two animals were highly vascularized, had the clinical appearance of trabecular bone, and varied in size within one animal. The two masses in each of two animals were approximately 3×2×1.5 cm and 1.5×1×0.5 cm in size. One additional animal demonstrated pronounced periosteal bone formation over one TGF-β site. It is significant that in over 430 titanium implant surgical procedures masses like these have never formed over the titanium implants. Histologically, this periosteal bone formation over five TGF-β sites in three baboons was similar to an actively healing, uncomplicated, fracture callus, i.e., morphologically normal, mature bone formation.

In general, the methylcellulose was well tolerated and no foreign body response was present in any of the four treatment sites. Additionally, no evidence of cytologic atypia or malignancy was found in either titanium implants or periosteal samples. 

What is claimed is:
 1. A method for generation of bone at a site of an animal where skeletal tissue is deficient comprising administering to the animal, locally at the site in the presence of an osteogenic cell source, an effective amount of a composition consisting essentially of TGF-β in a pharmaceutically acceptable carrier, provided that such composition excludes a bone morphogenetic cofactor, the composition being administered to the animal in an amount effective to induce growth of morphologically normal, mature bone at the site.
 2. The method of claim 1 wherein the TGF-β is TGF-β1, TGF-β2, TGF-β3, TGF-β4, TGF-β5, or latent TGF-β.
 3. The method of claim 1 wherein the TGF-β is TGF-β1.
 4. The method of claim 1 wherein if the site is a periodontal site, the osteogenic cell source is an exogenous source.
 5. The method of claim 1 wherein the excluded bone morphogenetic cofactor is one derived from a bovine bone source and has a molecular weight of about 28 Kd or 36 Kd.
 6. The method of claim 1 wherein the skeletal tissue is deficient as a result of surgical intervention, removal of tumor, ulceration, implant, or fracture.
 7. The method of claim 1 wherein the osteogenic cell source is dispersed whole bone marrow cells, perichondrium, periosteum, or a cell line.
 8. The method of claim 7 wherein the osteogenic cell source is naturally present at the site.
 9. The method of claim 7 wherein the osteogenic cell source is present in the TGF-β composition.
 10. The method of claim 1 wherein the carrier is a polysaccharide.
 11. The method of claim 1 wherein the composition allows for sustained release of TGF-β at the site.
 12. The method of claim 1 wherein the animal is a human. 